Being a stepparent can be difficult with well-behaved children. When the children are disrespectful, it's even worse. If you are a stepparent, it can feel impossible at times. There are, however, some things you can do to make it better. Here are some tips on how to deal when your stepson or stepdaughter is out of line:
Enlist the Biological Parents
If you really want things to change with your stepchild, the first thing you need is to have the biological parents on board with what is and isn't acceptable behavior. This will go even further if you can get both parents on board, because they have no one to play against each other. Speak to your spouse, and if you can, your spouse's ex and try and come to an agreement on what constitutes acceptable.
Set Clear Boundaries
Once you have everyone on board (or at least everyone you can get), then it's time to talk to your stepchild about your clear expectations. If they tend to forget, then consider writing a contract for them about where the line is between civil and rude. Make it simple but clear. For example: Insults are not okay. If you have a problem with something, then let us know how your needs are not being met, and propose a solution. Don't complain just to put people down.
Reward, Don't Punish
This is subtle, but important. You need to structure your home in a way that makes anything beyond basic necessities be seen as privileges. Good behavior, like respecting a stepparent, allows the privileges to be kept as part of the status quo. Bad behavior puts them on pause until three solid days of respect are gained. If they mess up, just start the three day clock over. They will catch on soon enough. This can be a more effective way of dealing with things than punishing singular incidents.
Make the Bio Parent the Bad Guy
This is one that is used in almost every child psychology philosophy. The bad guy needs to be the biological parent, or it turns into a good parent, wicked stepparent dynamic. All punishment and calling out should be done, as much as possible, by the parent. If the child starts to only be disrespectful when they are alone with their stepparent, then you may want to give the child a break from time alone with the stepparent. If they are the one who takes their child on playdates, picks them up from school instead of making them ride the bus, and brings them to other fun things, you can let that child know that these things will stop until they can be polite when alone with the stepparent.